The general goal is to understand the mechanisms and control of ion transport in gastric mucosa. Studies can be divided into two different areas. 1) Ca, cyclic AMP and stimulus-secretion coupling. We will measure 45Ca efflux out of the serosal side of the frog gastric mucosa in an attempt to correlate changes in this parameter with stimulation of HCl secretion and activation of membrane fusion events (evaluated using electronmicroscopy). The effects of Ca-free (EGTA) solutions as well as those of the Ca ionosphere A23187 will also be tested in both resting and actively secreting tissues in an attempt to discover whether intracellular Ca may also be involved with control of Cl permeability and transport. The involvement of cAMP in the different processes will be assessed indirectly by measuring adenylate cyclase activity in isolated surface epithelial cell-rich and parietal cell-rich fractions of piglet gastric mucosa. 2) Na-coupled Cl transport. The effects of the cation ionophere nystatin will be tested in an attempt to determine whether active, "non-acidic" Cl transport is generated by the turn-over of the Na-K pump or by a NaCl co-transport scheme. We will measure transepithelial voltages, resistance, current, and unidirectional fluxes of 36Cl and 22Na. We will also be interested in the interactions among HCO3, pH, NA and active Cl transport. The effects of solutions with different pH's and of different buffers with variable pK's and lipid solubilities will also be measured in an attempt to discover how HCO3 and Na ions are involved as stimulators of active Cl transports. In these latter studies, intracellular ionic activities will be measured using ion specific microelectrodes.